1. Field of the Invention
This invention concerns “foundation” brakes provided with drum brake shoe webs that are angled, or that “dogleg,” at anchor ends to establish more stable stances on drum brake anchor pins. The invention can be utilized in conjunction with standard drum brakes already in use, but is especially advantageous and cost effective when used in configurations having offset return springs.
2. Description of Related Art
An offset return spring configuration adds side loading to drum brake shoes and forces ends of the shoes to lift off of the anchor pin. Since a drum brake using an off-centerline return spring has unbalanced forces, the brake shoes tend to “rock” or tilt and lift off from one side of the anchor pin. Tilting of drum brake shoes in this manner causes many technical issues.
Brake shoes that somehow capture the anchor pin are currently used to eliminate this rocking or tilting. This is generally done by having a fully captured anchor pin. A web with a full 360° circle that hangs on to the anchor pin and keeps a shoe from lifting off is common.
In another way of capturing an anchor pin, four additional plates are used. These plates have two holes, with one of the holes designed to slip over the anchor pin and another of the holes designed to slip over a pin at the return spring hole. These plates “scissor,” so that each shoe has a plate on both sides (four plates per wheel end). The plates also keep the shoes from lifting off.
U.S. Pat. No. 1,667,375 to Dodge discloses a dogleg web shoe design intended to minimize manufacturing costs by having a set of dogleg-shaped pressed arms.
U.S. Pat. No. 2,928,510 to Kay concerns a brake shoe design in which anchor points on the web are also locating points for a spring to minimize brake distortion.
U.S. Pat. No. 4,773,512 to Murakami discloses a drum brake shoe with multiple reinforcement flanges to reduce noise. The flanges are paired over the length of the web to increase torsional rigidity and reduce noise.
German patent document DE 3818235 to Martin discloses a brake shoe web body that doglegs twice, but not in the same pattern. The purpose of the Martin pattern is to save weight.
U.S. Pat. No. 2,928,506 to Goldman discloses brake shoes with a central bridge on each shoe on which a return spring is affixed. This configuration improves anchor pin wear.
U.S. Pat. No. 3,877,141 to Bradshaw et al. concerns a method to make brake shoes with a single dogleg-style rib. The dogleg is added to improve casting.
U.S. Pat. No. 4,360,959 to Johannesen relates to a method for making a brake shoe from a single blank. Manufacturing is simplified by way of a dual rib feature, because welding is eliminated.
U.S. Pat. No. 4,732,240 to Flaim concerns a method to stabilize and improve drum brakes by changing brake pad lengths.
U.S. Pat. No. 5,515,952 to Jackson discloses a brake shoe with mass damping weights attached to reduce noise.
Finally, U.S. Pat. No. 6,336,533 to Pollock et al. shows a special spring mounted between web flanges to reduce noise and smoothly apply the lining to the drum.